Primary production of microphytobenthos in the Ems-Dollard Estuary

Abstract

From 1976 through 1978 primary production of microphytobenthos was measured at 6 stations on intertidal flats in the Ems-Dollard estuary using the 14C method. The purpose of the measurements was to estimate the annual primary production at different sites in the estuary and to investigate the factors that influence the rates of primary production. Therefore benthic chlorophyll a and a set of environmental factors were measured. Only primary production correlated sigruficantly with chlorophyll a concentration in the superficial (0.5 cm) sediment layer; other factors (temperature. in situ irradiance) did not correlate with primary production, primary production rate or assimilation number. Annual primary production ranged from ca. 50 g C m-' to 250 g C m-2 and was closely related to elevation of the tidal flat station. However, highest values were also recorded at the station closest to a waste water discharge point in the inner part of the estuary. Annual primary production can be roughly estimated from the mean annual content of chlorophyll a in the sediment. Use of different calculation methods results in annual primary production values that do not differ greatly from each other. Also productivity rates did not differ much over most of the estuary, except at the innermost station which showed a high production rate in combination with high microalgal biomass; this could not be explained by the high elevation of the station alone. A hypothesis is offered to explain the limited primary production of microphytobenthic vegetations.